During operation of a typical gas turbine engine, fuel may be supplied to a combustion section before being ignited to drive rotation of one or more turbines. In order to ensure proper combustion and/or power generation, a fuel metering and pressurization system is generally provided in operative association with the gas turbine engine. Typically, multiple hydro-mechanical valves are connected in series to regulate the amount of fuel delivered to the combustion section, as well as the pressure available for servo actuation. For instance, a fuel metering and pressurization system may include a fuel metering valve that sets the flowrate of fuel to a combustion section of an engine. A hydro-mechanical pressurization valve downstream from the fuel metering valve may control the pressure available for servo actuation. The hydro-mechanical pressurization valve may be referenced to the output of a fuel pump.
Within such conventional systems, fuel is typically circulated by a pumping unit tied to the operating speed of the engine. Excess fuel, or fuel in excess of that needed for combustion, is recirculated to one or more bypass circuits. Moreover, in the case of some fuel metering and pressurization systems, fuel within one or more bypass circuits can be directed to/from a variable geometry component, such as a variable guide vane, of the engine. The force or pressure used to actuate the guide vane may, thus, correlate to fuel pressure within the system. In turn, this force or pressure may vary according to the changing demands of the aircraft.
However, existing systems must often accommodate occasions in which demands for actuating the variable geometry components are misaligned with the fuel demand of the combustion section. Fuel demand at the combustion section may limit fuel flow within the fuel metering and pressurization system faster than the engine speed, and, thus, may limit fuel flow faster than the actuation force needed to move the variable geometry components is reduced. In the case of a rejected takeoff event, fuel demand at the combustion section may significantly decrease fuel flow faster than the pressure required for actuating a variable geometry component.
In order to accommodate for such variations in demand, existing systems are often sized and configured to accommodate conflicts between pressure requirements of an engine's variable geometry components and its combustion section. Bypass valves and circuit members, such as actuators, pumps, and heat exchangers, thus, are often configured to be oversized. The increased size allows for a required actuation force to be achieved with reduced fuel system pressures available for actuating a variable guide vane, even when fuel flow is suddenly limited. Nonetheless, existing oversized configurations can result in significant weight being added to the engine. Moreover, the increased size of a system's constituent elements may result in increased amounts of power being drawn from the engine. Drawing power to circulate fuel may reduce the amount of power available for propulsion, decreasing overall engine efficiency. Furthermore, the increased circulation of fuel may result in increased amounts of heat being carried by the fuel within the system.
Accordingly, there is a need for a fuel system that can provide adequate fuel pressurization to various portions of an engine, without requiring significantly oversized elements. There is further need for a fuel system that can reduce power demands over the fuel system and increase overall engine efficiency and/or reduce engine weight.